When young healthy men eat fewer calories than they burn, their bodies burn slightly more energy at rest than expected based on the muscle they lose, suggesting other biological changes are contributing to this effect.

In physically trained men, a calorie deficit prevents any increase in resting metabolic rate, even when a lot of exercise is performed.

When young healthy men consume 50% more calories than they burn, their resting metabolic rate rises, even if their physical activity levels stay the same.

When adults cut calories for a long time, their bodies may respond by increasing hunger and slowing metabolism, making it harder to keep losing weight.

In trained men, resting metabolic rate increases only when both physical activity and food intake are high and balanced, not when calorie intake is higher or lower than expenditure alone.

After losing weight, obese adults who maintain higher levels of physical activity and food intake have a slightly higher resting metabolic rate than those with lower activity and intake, resulting in an increase of about 79 calories burned per day at rest.